(1) Field of the Invention
The present invention relates to a power steering apparatus for a wheeled vehicle, and particularly for an agricultural tractor.
(2) Description of the Prior Art
As disclosed in U.S. Pat. No. 4,592,440, for example, a power steering apparatus for a tractor comprises an axle oscillatably supported by an axle frame through a center shaft, steerable wheels attached to opposite ends of the axle through kingpins, and a power cylinder including a cylinder tube extending parallel to the axle. The power cylinder includes piston rods each connected to a steering arm through a turn buckle acting as a tie rod.
In the above known construction, however, the tie rod having two joints is connected to each piston rod at an extreme end of the power cylinder. Such tie rods are formed short since a long distance is taken up transversely of the tractor from the extreme end of one of the piston rod and to extreme end of the other piston rod. This allows only a small distance for tread adjustment.
Since the tube of the power cylinder extends parallel to the axle and the steering arms oscillate in three-dimensional directions, the tie rods each having two joints must be used for the connecting purposes in order to absorb such oscillations.
With the above construction, there is a limitation to reduction of the tread because the power cylinder and the tie rods at least require their accommodating spaces transversely of the tractor. There is a further disadvantage in that a loss will occur in the transmission of a steering force to the steering arms.